Grading or separation of particles of solids, liquids, or gases



Jan. 11, 1944. MUTCH 2,338,779.

GRADING OR SEPARATION OF PARTICLES OF SOLIDS, LIQUIDS, OR GASES 2Sheets-Sheet 1 Fig.1.

Filed Jan. 24, 1940 i 1 i. l

INVENTOR N. MUTCH N. MUTCH Jan. 11, 1944.

GRADING OR SEPARATION OF PARTICLES OF SOLIDS, LIQUIDS, OR GASES FiledJan. 24, 1940 2 Sheets-Sheet 2 INVI-INTOR N. MUTCH aww 1PM ATTYs,

Patented Jan. 11, 1944 GRADING OR SEPARATION OF PARTICLES OF SOLIDS,LIQUIDS, OR GASES Nathan Mutch, London, England Application January 24,1940, Serial No. 315,451 In Great Britain January 27, 1939 7 Claims.

This invention comprises improvements in or relating to the grading orseparation of particles of solids, liquids or gases.

It is an object of the invention to grade solid particles or liquiddroplets or gas bubbles dispersed in a fluid medium (liquid or gas) onthe basis of size and density.

In the past such grading has been attempted in several ways:

(1) sieving;

(2) Washing and sedimentation;

(3) The addition of electrolytes to suspensions by which means anelectric charge is imparted to the finest particles, e. g., kaolin inwater. Separation has then been accomplished either by causing thesmaller charged particles to move in an electric field or by allowingthe larger uncharged particles to fall under the influence of gravity.

(4) Simple centrifugalisation.

The present invention comprises a process of grading or separation ofparticles dispersed in a fluid medium characterised by the fact that thedispersion of particles and medium is subjected to centrifugal force andthe medium is caused to flow in a contrary direction to the tendency tomotion of the particles under the action of centrifugal force, at acontrolled speed such that particles of a size greater than that whichit is desired to retain in the medium (or of a density which difiersmorewidely from that of the fluid medium) are unable to move with the mediumagainst the action of centrifugal force while flner or less denseparticles move with it and are thereby separated from the others. It isto be understood that under the term particles there is included notonly solid particles but also liquid droplets such as the droplets of amist or of oil in a suspension in water and also minute gaseous bubblessuch as the bubbles in a foam. When the particles are heavier (denser)than the fluid in which they are dispersed they tend, under the actionof centrifugal force, to move outwardly and the fluid medium will,therefore, in accordance with the present invention, move inwardly in acontrary direction to the tendency of motion of the particles. On theother hand, when the particles are lighter than the fluid, as is thecase with a foam of air bubbles or a suspension of oil droplets inwater, the tendency is for the particles to move inwardly when thedispersion is subjected to centrifugal force and in this case the fluidmedium will be allowed to move outwardly at a controlled rate under theaction of centrifugal force, the 5 rate of outward movement of the fluidbeing such as to lead to the desired separation of the larger bubbles ordroplets from the smaller ones.

Preferably the radial velocity of the dispersion is made, between twoselected radii, to vary inversely as the radius so as to form a zone inwhich the tendency to separation is constant throughout the zone. By thetendency to separation being constant is meant that the criticaldifferentiation of the particles which is effected is the samethroughout the zone. That is to say, if particles of a size or densitya: are rejected at one part of the zone they would equally be rejectedat another part of the zone of smaller radius. This greatly assistscritical separation.

A plurality of different zones in which the radial velocity of thedispersion varies as just de scribed may be provided one within another,through which the dispersion passes in succession, said zones beingseparated by zones of collection wherein separated particles arecollected from the dispersion. As already indicated the invention may beapplied to various types of dispersion. For example, it may consist of amist of liquid droplets suspended in a gas and such a suspension may bepassed through the separation zone inwardly against the action ofcentrifugal force andthereby be relieved at the outer edge of theseparation zone of heavier or denser droplets. Again, the dispersion mayconsist of a suspension emulsion or foam wherein the "particles arelighter than the liquid medium and the movement of the liquid is acontrolled outward flow, th larger bubbles or droplets, as the case maybe, being prevented from flowing outward by the effect of centrifugalforce while the smaller bubbles or droplets move with the liquid. Thenagain the dispersion may consist of solid or liquid particles suspendedin a liquid of lighter specific gravity than the particles and then thedirection of flow of the liquid is inward, so that heavier or denserparticles are left at the outer edge of the separation zone. Finally, itmay consist of solid particles suspended in a gas and the gas may flowinwardly against the action of centrifugal force, whereby heavier ordenser particles are separated at the outer edge of the separation zone.

While the separation of larger or denser particles has been hereinabovereferred to it will. be understood that the separation will follow theknown laws depending on the viscous drag of the liquid on the particleson the one hand and the centrifugal force exerted by the rotation of the"particles on the other hand, this force being in the present inventionsubstituted for that of gravity which latter obtains in knownclassification processes. The substitution of cent ifugal force for theforce of gravity has the advantage that the force applied to theparticles can be readily controlled whereas gravitational force isconstant and limited. As is known the separation therefore depends notonly on the density of the particles and not only on their size, but

on both factors, and also of course partly upon v their shape, and theconditions of the process will in practic be regulated, if necessary, bypreliminary experimental tests so as to obtain the best results. For thesake of simplicity in this specification in many cases the separation oflarger from smaller particles is referred to but it is to be understoodthat this is not intended to l mit the use of the apparatus to caseswhere the par ticles" are all of the same density and size alonedetermines their separation.

. .An important and particular application of the invention is to thetreatment of mists of liquids having germicidal properties, or which arelethal to insect carriers of disease or having therapeutic properties.In this connection the invention comprises a process for the treatmentof such mists consisting in subjecting the mist to the action ofcentrifugal force while causing it to flow inwardly against thecentrifugal force at such a rate that only droplets of the liquid of asize smaller than a predetermined size are carried inwardly against theaction of centrifugal force, so that the mist is separated from coarserparticles and thus the quantity of liquid necessary to produce a givennumber of droplets per unit volume is reduced.

The invention further includes apparatus for carrying out processes a:set forth above, characterised by the provision of a rotating memberhaving one or more passages for the dispersion to be separated having aradial component to their direction, means to feed the suspension to oneend of said passage or passages, means to draw 01! the suspension fromthe other end of said passages and means to collect larger separatedparticles from the periphery of the path of the entrance end or ends ofsaid passage or passages.

The following is a description by way of example of certain forms ofapparatus in accordance with the invention and of the process as carriedout therein:

In the accompanying drawings:

Figure 1 is a diagram showing one form of separating passage;

Figure 2 is another diagram showing another form;

Figure 3 is a horizontal section through the centre of a completeapparatus;

Figure 4 is a section upon the line 4-4 of Figure 3;

Figure 5 is a detail showing a modification;

Figure 6 is a view similar to Figure 3 of a modifled form of apparatus,and

Figure 7 is a half-section through a further modified form.

Referring to Figure l, the chain line XY is to be regarded as an axis ofrotation about which there may be rotated the tube II which is so shapedthat its cross-sectional area is inversely proportional at all points toits distance from the axis XY. It follows that if the tube is revolvedabout the axis KY and a fluid medium containing particles in suspensionis passed through the tube toward the axis, the velocity of thesuspension will at all points be directly proportional to thecentrifugal force exerted upon it. The centrifugal force exerted onsolid or liquid droplets (if of higher density than the medium) willtend to make them move outwardly but the inward flow of the suspendingliquid will tend to carry them in with it, that is to say, thesuspending fluid will exert a frictional drag on the particles. If weassume that this drag is directly proportional to the relative speedbetween the fiuid and the particles then the size of particle which canbe dragged inwardly by the suspending fluid is with a tube of the shapedescribed the same at all radii. Therefore larger particles than thosewhich at a particular speed can be dragged inwardly will all fly out ofthe tube under the action of centrifugal force while smaller particleswill all be drawn in. If th law of friction (or viscosity) between thesuspending fluid and the particles is not one of direct proportionalitythis can be allowed for by a corresponding variation in the shape of thetube.

If we suppose that the tube is not shaped as in Figure 1, but is, say,cylindrical, separation is still effected but what happens is that anycoarse particles which succeed in passing inwardly beyond a particularplane will thereafter be carried inwardly w th still greater certaintybecause the centrifugal force upon them is decreasing. Therefore thecertainty of removal of the coarse particles is not so great. On theother hand, if the tube is flared too much it may be that fine particleswill tend to collect in a cloud at the wider end without being properlycarried away. Any corrections to the particular shape of the tube whichexperience might dictate could readily be adopted after tests and itwill be seen at once that in principle it is possible to mount a numberof such tubes pointing radially outwards about a supporting spindle andto pass large quantities of a suspension inwardly through them, thetubes at any particular speed rejecting particles which are larger thanthose which can be carried inwardly against the action of centrifugalforce. If the particles in a suspension are not all of the same densitythen the denser particles will tend to be thrown out in a mannerparallel to the well known effects which occur in gravity classificationapparatus, but in the present invention there is substituted for gravitythe much greater and readily controllable force due to centrifugalaction. If the liquid to be separated is a foam or an emulsion in whichthe particles are lighter than the suspending liquid the sameconsiderations apply but the direction of motion is reversed.

Referring to Figure 2, this shows a tube l2 rotating about an axis XY asin the case of Figure 1. In this case the section of the tube lyingbetween the planes A and B is made of a crosssection which variesinversely with the radius or has an experimentally determined functionalrelationship therewith as already described so that the tendency toseparation in the zone from A to B is constant. Between the planes B andC the tube is made to expand more rapidly and thus the maximum size ofparticles which will pass through the section from A to B will refuse topass through the section from B to C and such particles of maximum sizewill collect at the plane B and from here they can, by suitable means bewithdrawn, permitting only the finer particles to pass on into thesection from plane C to plane D. This zone expands once again inaccordance with the same law as the zone from A to B. As the speedthrough this zone is slower than through the zone from A to B it acts asa filter which allows only finer particles to pass. The expansion fromplane D, to plane E is more rapid than the separation law prescribes andtherefore the least fine particles which pass the plane D will tend tocollect at this plane, leaving only still finer particles to pass onbeyond the plane E. By such a tube, with appropriate means of removal atthe planes B and D several grades of particle can be produced. That isto say, .the coarsest particles are removed at the entrance plane A, aless coarse grade at the plane B, a finer grade at the plane D and thefinest material passes on in the suspension past the plane E. Thereis afurther removal at plane F if the passage is given a further change oftaper at this point as may be done and is shown in the drawings. Furtherplanes of removal may be arranged after plane F if desired..

Figures 1 and 2 are diagrammatic. It is necessary to provide means forthe introduction of the medium and the particles in it into the tubes insuch a way that they enter with the least possible shock, as otherwisethey tend to be shaken out of suspension. Moreover, the whole flow ofthe medium and its dispersed particles must be kept as smooth aspossible everywhere. Figures 3 to 6 indicate apparatus which has beendesigned to embody the principles of Figures 1 and 2 in a practicalform.

Referring to Figures 3 and '4, these show an apparatus comprising fourinlet passages I3 which surround a rotating separating wheel I 4provided with curved peripheral blades IS. The fiuid medium carrying theparticles to be treated is lead on to theblades by the ducts l3 and thespeed of the medium-is arranged to be nearly equal in a circumferentialdirection to the tip speed of the blades l5, the speeds being soarranged as to minimise turbulency at the point of entry into'the wheel.As can be seen from the cross-section in Figure 4, the wheel I4comprises upper and lower walls I6, H which diverge from the edge towardthe centre and the divergence is made such that the area increases in aregular proportion in accordance with the requirements of separationalready expressed. Thus material larger than a particular size is unableto reach the interior of the wheel but is held near the blade tips.

It will be appreciated that suitable means should be provided to impartan appropriate speed with suspension and to keep the wheel running atits proper speed. As the medium is led on to the blades at the samespeed as these latter, no appreciable pull is exerted by the medium onthe blades or by the blades on the medium and each must be separatelyset and kept in motion.

Between the inlets [3 the casting approaches the tips of the bladesclosely as at i8 in the figure and in the surfaces l8 there are outletducts l9 into which the coarser material is thrown by the blades as soonas they pass out of communication with the inlets I3. From the ducts l9there are suitable exits for the coarser material in a direction at anangle to the plane in which the section of Figure 3 is taken. Thus thelarger material is removed from the ducts I9 and the suspension with thefiner material passes towards the centre where it is allowed to flow outthrough an outlet (Figure 4) or is withdrawn by some form of suctiondevice.

A certain amount of coarse or heavy material may tend to be thrown outand collect upon the outer walls of the inlets l3 and if desired adrawoif conduit 2| (Figure 5) may be provided to permit of thecollection and recovery of this material and prevent it from interferingwith the operation of the device.

Referring to Figure 6, this shows an apparatus which is in generalsimilar to that of Figure 3, comprising a rotary separating wheel llhaving blades l5 but in this case it is assumed that the inlets to thecasting, indicated by numeral 22, are in a plane other than that shownby the section. The material is in this case guided on to the blades l5by fixed external guide blades 23 and the coarser particles I areremoved through ducts 24.

Figure '7 shows another alternative apparatus in which the wheel I4carrying blades I5 is provided with a lateral inlet opening 25 ofannular form at one side of the blades. The dispersion to be treated isdirected into the blades thrqugh this opening by inclined guides 25 froma feed chamber 21 below the wheel l4. Coarser material is rejected intoan outer annular collecting space 28 and the fine suspension passes outthrough the centre exit 29.

It will be understood that if foams or emulsions of liquids lighter thanthe medium are being treated the exits 20 or ZED-would become inlets andthe inlet conduits I3, 23 or 26, as the case may be, would becomeoutlets.

As will be appreciated, it would be possible to make the contour of thewheel l4 stepped like Figure 2 if desired and to provide outlets in theside of it at suitable places similar to the openings 25.

In addition to the application of the invention to the use of germicidesand the like as already described it may be applied if desired to thepro duction of fine mists for other purposes.

The production of fine even foams has already been referred to and theseparation or grading of all kinds of solid matters suspended in liquidsor gases is another field of application of great practical importance.

I claim:

1. A process of grading particles dispersed in a fluid medium comprisingintroducing the dispersion of particles and medium into a rotating vanedwheel with an initial velocity in the directionof rotation of the wheelsubstantially equal to the velocity of the vanes at the point of entrythereto so that it enters between the vanes thereof without shock,subjecting the dispersion in the wheel to centrifugal force, causing themedium to flow in a direction contrary to the tendency of motion or theparticles under the action of centrifugal force at a control-led speedsuch that particles of size greater than that which it is desired toretain in the medium, and particles of a density which differs morewidely from that of the fluid medium, are unable to move with the mediumagainst the action of centrifugal force while finer particles, and thosediffering less widely in density, move with it and are thereby separatedfrom the others, said dispersion being passed successively through anumber of different zones in each of which between two selected radiithe radial velocity of the dispersion varies inversely as the radius,said zones being separated by zones of collection wherein separatedparticles are collected.

2. Apparatus for grading particles dispersed in a fluid medium,comprising a vaned wheel having passages between the vanes for thedispersion to be graded, a casing surrounding the vaned wheel and havingtangential passages to feed the dispersion, the walls of the passagesclosely approaching the periphery of the wheel at separated pointsaround the periphery, and means for drawing oif separated particles atthe places where the walls of the passages approach the periphery of thewheel.

3. Apparatus for grading particles dispersed in a fluid medium,comprising a vaned wheel having passages between the blades for thedispersion to be graded, a casing surrounding the vaned wheel and havingtangential passages or guide blades to feed the dispersion, the walls ofthe passages closely approaching the periphery of the wheel at separatedpoints around the periphery of the wheel, outlet means for separatedparticles spaced apart from the tangential passages by portions of thecasing which are of sufflcient length in a peripheral direction to blankoff the outlet means from connection with the tangential passages orguide blades.

4. ,A process of grading particles dispersed in a fluid mediumcomprising introducing the dispersion of particles and medium in streamline flow tangentially'at a plurality of circumferentially spaced zonesabout a rotating varied wheel into closely juxtaposed flow paths betweenthevanes extending substantially radially of the wheel and whichjuxtaposed paths comprise the major portion of the circumference of thewheel and which 'zones of introduction have a circumferential extentgreater than that of the spacing between them, and with an initialvelocity in the direction of the wheel rotation substantially equal tothat of the vanes at the points of entry thereto, flowing the mediumthrough the flow paths in the vaned wheel in a direction contrary to thecentrifugal force exerted thereby on said medium and thereby subjectingparticles in said medium to the opposing actions of centrifugal forceand viscosity drag of the flowingmedium, varying the cross-sectionalarea of at least a substantial length of the stream of dispersion insaid wheel in such manner that the velocity of flow is proportional tothe centrifugal force whereby particles of mass properties such thatcentrifugal action thereon predominates over viscosity drag areseparated throughout said length of stream, removing the thus separatedparticles at circumferentially spaced regions intermediate said spacedzones of introduction, and removing the medium with the remainingdispersed par-' ticles at the end of said length of stream.

5. Apparatus for grading particles dispersed in a fluid medium,comprising a wheel having vanes of concavo-convex section formingpassages tor the dispersion while being graded, a casing surroundingsaid wheel and having a plurality of inlet ducts arranged tangentiallyto said wheel and a plurality of outlet ducts for separated particlesalternating with said inlet ducts, an outlet duct for said dispersionafter being graded, and means for driving said wheel.

6. Apparatus for grading particles dispersed in a fluid medium,comprising a wheel having vanes of concavo-convex section arranged forthe passage of the dispersion while being graded, a casing surroundingsaid wheel and having inlet chambers for the dispersion and outlet ductsfor separated particles alternating in the casing, said chambers andducts having walls in juxtaposition to the periphery of said wheel,guide blades for said dispersion arranged in said inlet chambers, outletmeans from said casing for said dispersion after being graded, and meansfor driving said wheel.

7. Apparatus for grading particles dispersed in a fluid mediumcomprising, a wheel having vanes for passage of the dispersion whilebeing. graded each of said passages formed by the vanes havingalternating zones for separation and collection of separated particles,ducts in said casing for receiving particles from said collection zones,outlet means on said casing for said dispersion after being graded, andmeans for driving said wheel.

NATHAN MUTCH.

